1. Technical Field
This invention presents devices and methods for inspection and repair of piping, such as fluid distribution means, and more particularly, devices and methods for inspecting gas mains without interrupting gas service during the testing operation. Certain novel collapsible support mechanisms (or centralizers) for such an inspection device are specifically described herein.
2. Description of the Prior Art
The transportation of natural gas, water, petroleum products, and other gases and fluids typically involves the use of pipelines, often of considerable lengths. Cross-country pipelines are, of course, of large diameters such as 12 inches, 24 inches and 30 inches in capacity. Such pipeline sizes are usually associated with the transporting of natural gas, and large sizes of pipes are normally fabricated of steel. In urban areas distribution of natural gas, and the distribution of manufactured gas in previous years, is accomplished through vast networks of smaller size buried pipe, principally of four, six, eight and ten inch diameters. While present installation of underground pipe utilizes plastic, particularly natural gas pipes of four, six and eight inch diameter size, thousands of miles of cast iron and steel pipe have been installed and buried over the years, and are presently in use for the delivery of natural gas. In most of the United States cast iron and steel gas distribution lines are often four inches in diameter and typically include many 90 degree corners. Common problems encountered with buried cast iron and steel pipe include deflection of the pipe caused by settling of the earth around the pipe, heaving due to frost (or forces applied to the earth around the pipe) causing leaking at joints or cracking of the line and, often, the collection of water therein. In addition, corrosion leaks in steel mains are common.
While numerous devices exist for the visual or other inspection of the interior of a pipeline, most, if not all, existing techniques have disadvantages which make their use at best inconvenient and, in all likelihood, difficult, time consuming and/or expensive. Many in-line pipe inspection devices and methods require, for example, in the case of gas pipe lines, discontinuance of service and/or severing of the main for insertion of the inspection device into an open end of the main, which is a complicated and costly process involving bypass and shut-off procedures. Obviously, this technique is expensive both in terms of the interruption to the gas service and the damage caused to the gas main. Inspection devices so inserted typically include a fixed centralizer feature for maintaining the in-line viewing assembly substantially concentric with the axis of the pipe.
In the above-incorporated application, entitled "Internal Pipe Inspection System," a collapsible centering mechanism is described for supporting the device inspection/repair head once inserted into a gas main. The novel inspection/repair head disclosed therein is inserted into a live gas main (without requiring an interruption of service to customers connected to the line) through an opening, such as an existing lateral service opening, in the line smaller than the internal diameter of the pipeline. To accomplish this object it is essential that the support mechanism for the inspection/repair head be readily collapsible and/or bendable. The extent of collapsibility is particularly significant for gas mains since lateral customer service lines typically tap into a main line via an opening that is one-third or less the size of the internal diameter of the pipeline. For example, one inch and one and one-quarter inch diameter lateral openings are common in four inch and six inch gas distribution mains in the United States.
One preferred centering technique described in the incorporated application is the use of rigid, outwardly biased legs extending from the central inspection/repair head and pivotally secured to the body so as to manually collapse thereto. If desired, skids can be hingedly secured to the free ends of the outwardly extending legs, again so as to collapse towards the main inspection/repair head when manually actuated (i.e., upon insertion and removal of the inspection/repair head through a restricted opening in the pipe). Various other centering approaches are also described therein.
Continuing research into an internal pipe inspection device such as described in the incorporated application has resulted in an improved support mechanism (centralizer) having a low profile mounting, simple design and ready adjustability to pipes of different internal diameter. This commercially significant design is a principal aspect of the present disclosure.